This invention relates to identification and enumeration of morphologically indistinguishable cells which have different membrane characteristics. More particularly, the invention relates to a method for the identification of subsets of lymphocytes by labeling the cells with selected strains of bacteria which, when brought into close contact with the cells, remain firmly attached and function as labels or markers.
The most widely used methods for identifying subpopulations of cells include the use of specific antibody to detect surface antigens, sedimentation velocity, electrophoresis, and the binding of heterologous erythrocytes. Such methods, however, present a number of disadvantages, such as complexity, cost and inability to distinguish among closely related cell types.
It is known (Ghetie et al., Europ. M. Immunol. 4, 500, 1974) that the bacterial strain of Staphylococcus aureus, Cowan I, has the ability to bind to the Fc portion of IgG, thus making it possible to identify cells bearing IgG on their surfaces, although such cells could also be identified by other methods described above. This property of the Cowan I strain of Staphyloccus aureus has been looked upon as a not-too-surprising curiosity, since the Fc region of IgG is recognized by other structures such as the Fc receptors on some leukocytes, the first component of complement, and the placental barrier.